1. Field of the Invention
The present invention relates to three-dimensional printing apparatuses.
2. Description of the Related Art
A three-dimensional printing apparatus is conventionally known in which a liquid photo-curable resin stored inside a tank is irradiated with light so as to cure the photo-curable resin, thus forming a three-dimensional object. A three-dimensional printing apparatus of this type includes a base, a tank, and a raisable and lowerable holder. The base is provided with an opening. The tank is placed on the base. The holder is disposed above the tank. An optical device including a light source and a mirror, for example, is disposed below the base. Light emitted from the light source is reflected by the mirror. A resin inside the tank is irradiated through the opening of the base with the light reflected by the mirror. A portion of the resin inside the tank which has been irradiated with the light is cured. By controlling a light irradiation position, a position at which the resin is to be cured is appropriately changed. Hence, the cured resin can form a desired cross-sectional shape. A desired cross-sectional shape is continuously formed downward by sequentially raising the holder. As a result, a desired three-dimensional object is formed by the cured resin.
In the above-described three-dimensional printing apparatus, the tank that stores a photo-curable resin in liquid form is placed on the base before a three-dimensional object is formed. After the three-dimensional object has been formed, the tank in which the photo-curable resin in liquid form remains is moved from a position on the base. In this case, the photo-curable resin might scatter from the tank. The scattered photo-curable resin might adhere to the optical device through the opening. A known solution to this problem is to close the opening with a transparent plate made of glass, for example, so that the scattered resin does not pass through the opening.
However, when the opening is closed with the transparent plate, the light emitted from the light source is undesirably attenuated through the transparent plate before being applied to the photo-curable resin, thus disadvantageously preventing the resin inside the tank from being efficiently cured. Furthermore, the resin scattered from the tank might adhere to the transparent plate. The resin adhered to the transparent plate might block the light emitted from the light source.
A proposed solution to these problems is to provide the opening with a shutter that is controllable so as to be opened and closed. JP 2012-187807 A discloses a three-dimensional printing apparatus that includes a sensor that detects whether or not a tank is placed on a base, and a motor that drives a shutter so that the shutter is opened and closed. The sensor includes a protrusion that can be protruded from and retracted into the base, and a spring that constantly urges the protrusion upward. Upon placement of the tank on the base, the protrusion is pushed down by a bottom wall of the tank. Thus, the protrusion is retracted into the base. Upon removal of the tank from a position on the base, the protrusion protrudes from the base due to a force of the spring. The sensor detects whether or not the tank is placed on the base on the basis of a state of the protrusion. In this three-dimensional printing apparatus, upon detection of placement of the tank on the base, the shutter is automatically opened by the motor. In contrast, upon detection of removal of the tank from the position on the base, the shutter is automatically closed by the motor.
The three-dimensional printing apparatus disclosed in JP 2012-187807 A is arranged so that the tank is placed on the base from above in such a way as to push down the protrusion. Therefore, when the tank is placed on the base, a gap might briefly be provided between the tank and the base, with the shutter opened. When the tank is moved away from the base, a gap might also be provided between the tank and the base, with the shutter opened. Thus, a photo-curable resin might enter through the gap. As a result, the photo-curable resin might adhere to an optical device.